Lin, Youlin (Mallinckrodt Medical, Inc.). Medical examination of soft tissues or organs by nonsurgical means often requires the introduction of a special agent that makes the detection system responsive to detail in the tissue of interest. Radiopaques, often called x-ray contrast media, are examples of such diagnostic agents. Radiopaques are categorized according to specific applications, such as angiog., urog., myelog., cholecystog., cholangiog., gastrointestinal radiog., computed tomog., arthrog., and hysterosalpingog. The importance, chem., and kinds of radiopaques developed for the types of medical imaging are presented. The evolution of research efforts from high osmolality contrast media (HOCM) to low osmolality contrast media (LOCM) is emphasized. Historical perspectives, cost considerations, and future outlooks in contrast media development are briefly outlined. Phys. constants, such as osmolality, water solubility, viscosity and partition coefficient, and median LD in animal studies are cited and compared for selected contrast agents. Sources are listed for com. radiopaque suppliers in the United States. Volume 20, pp. 906-930, 129 references to Dec. 1995.